Compressing resources with gzip or deflate can reduce the number of bytes sent over the network

Problem:
Using Google PageSpeed Insights to measures the performance of a page for mobile devices and desktop devices.

There is a suggestion "Compressing resources with gzip or deflate can reduce the number of bytes sent over the network."

You could refer to Google's "Enable compression" suggestion

Solution:
To resolve this problem on Apache server, please try to enable gzip compression by modifying your .htaccess file.

# ######################################################################
# # WEB PERFORMANCE                                                    #
# ######################################################################

# ----------------------------------------------------------------------
# | Compression                                                        |
# ----------------------------------------------------------------------

<IfModule mod_deflate.c>

    # Force compression for mangled `Accept-Encoding` request headers
    # https://developer.yahoo.com/blogs/ydn/pushing-beyond-gzipping-25601.html

    <IfModule mod_setenvif.c>
        <IfModule mod_headers.c>
            SetEnvIfNoCase ^(Accept-EncodXng|X-cept-Encoding|X{15}|~{15}|-{15})$ ^((gzip|deflate)\s*,?\s*)+|[X~-]{4,13}$ HAVE_Accept-Encoding
            RequestHeader append Accept-Encoding "gzip,deflate" env=HAVE_Accept-Encoding
        </IfModule>
    </IfModule>

    # - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

    # Compress all output labeled with one of the following media types.
    #
    # (!) For Apache versions below version 2.3.7 you don't need to
    # enable `mod_filter` and can remove the `<IfModule mod_filter.c>`
    # and `</IfModule>` lines as `AddOutputFilterByType` is still in
    # the core directives.
    #
    # https://httpd.apache.org/docs/current/mod/mod_filter.html#addoutputfilterbytype

    <IfModule mod_filter.c>
        AddOutputFilterByType DEFLATE "application/atom+xml" \
                                      "application/javascript" \
                                      "application/json" \
                                      "application/ld+json" \
                                      "application/manifest+json" \
                                      "application/rdf+xml" \
                                      "application/rss+xml" \
                                      "application/schema+json" \
                                      "application/vnd.geo+json" \
                                      "application/vnd.ms-fontobject" \
                                      "application/x-font-ttf" \
                                      "application/x-javascript" \
                                      "application/x-web-app-manifest+json" \
                                      "application/xhtml+xml" \
                                      "application/xml" \
                                      "font/eot" \
                                      "font/opentype" \
                                      "image/bmp" \
                                      "image/svg+xml" \
                                      "image/vnd.microsoft.icon" \
                                      "image/x-icon" \
                                      "text/cache-manifest" \
                                      "text/css" \
                                      "text/html" \
                                      "text/javascript" \
                                      "text/plain" \
                                      "text/vcard" \
                                      "text/vnd.rim.location.xloc" \
                                      "text/vtt" \
                                      "text/x-component" \
                                      "text/x-cross-domain-policy" \
                                      "text/xml"

    </IfModule>

    # - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

    # Map the following filename extensions to the specified
    # encoding type in order to make Apache serve the file types
    # with the appropriate `Content-Encoding` response header
    # (do note that this will NOT make Apache compress them!).
    #
    # If these files types would be served without an appropriate
    # `Content-Enable` response header, client applications (e.g.:
    # browsers) wouldn't know that they first need to uncompress
    # the response, and thus, wouldn't be able to understand the
    # content.
    #
    # https://httpd.apache.org/docs/current/mod/mod_mime.html#addencoding

    <IfModule mod_mime.c>
        AddEncoding gzip              svgz
    </IfModule>

</IfModule>

The following snippet code extracted from sample configuration files of Apache HTTP server boilerplate configs project
Next, you can also use this Gzip compression test tool to check if gzip compression is enabled on your site or not.