Hello Jonwjr. We know the importance of ensuring your phone is working properly. We want to do all we can to help. How long have you been experiencing this issue? Are the applications that the phone freezes up on using data? Or related in some way? How are your calls and texts processing?
While some say it's not necessary on an iPhone, close most of the open apps, if there are a lot. Next try a soft reset......press and release the volume up button, then the volume down button, then hold the power button. Keep it pushed in. The phone will power down then release the button when it powers back on.