I feel your shit-uation.
Experienced the same issue.
So, I disabled the stock phone and messaging apps (and other android features apps).
Googled around and installed (then UNinstalled) several Play Store 4-stars rated phone, messaging and contact management apps.
Settled on 4pda and xda community project app developed 2013 called - True Phone (1.7.1 rev 89) app because of its built-in contacts phone, etc. info management feature.
Although it 'contains ads' I haven't yet seen any. Still, I will likely opt-in and pay ('help a starving developer') $1.99 for the ads free version.
Well, onward!
When I try to open the ’phone app I get the message “Phone has stopped” with a button “Open app again”. When I tap on that button I get the message “Phone keeps stopping” with a button “Close app”.
I have restarted and powered off and powered up again to no avail. This is recent behaviour. The ’phone can see the network and downloads data.
Any clues?