What will Reset Network Settings do to my phone?

Hello,

Reset Network Settings: Only network settings are removed.

When you reset network settings, previously used networks and VPN settings that weren’t installed by a configuration profile or mobile device management (MDM) are removed. Wi-Fi is turned off and then back on, disconnecting you from any network you’re on. The Wi-Fi and Ask to Join Networks settings remain turned on.

To remove VPN settings installed by a configuration profile, go to Settings > General > Profiles & Device Management, select the configuration profile, then tap Delete Profile. This also removes other settings and accounts provided by the profile. For more information, see Profiles settings in this guide. To remove network settings installed by MDM, go to Settings > General > Profiles & Device Management, select the management, then tap Remove Management. This also removes other settings and certificates provided by MDM. For more information, see “Mobile device management (MDM)” in the iOS Deployment Reference.

From:

Reset iPhone settings - iPhone User Guide