Before doing a reset, make a full backup in iTunes. If your contacts are only on your phone and not synced to iCloud or another cloud service like Gmail/Google; then you will lose your contacts.
For the calls, I'd block those numbers unless you know who is calling. Does the ringer not work for every single call, or just some? Resetting may help solve the problems you're having, but it can be time consuming; so if you can solve the problems without a reset then may want to try that first.
Doing a phone restart may help, and I'd suggest trying that first before going down the full reset path.
https://support.apple.com/en-us/HT201559