I keep getting cannot verify server identity. How doni stop this from popping up on my phone

That means that one or more services on your phone is trying to access an Internet service that has been shut down or is not secure. Most frequently these are subscription calendars that have expired, such as sports team schedules. So the first thing to do is to go to Settings/Calendar/Accounts/Subscribed Calendars and see if there are any there that are too old.

Also look at the name of the server in the message; that can be a hint to what the problem is.

Note that you can also get this message if you don’t have any Internet connection.