A customer asked me to test this behavior and sure enough when using the Phone tab, if you try to type the + sign it is reported as Character not valid. If you type too fast and add digits the error goes away yet the number won't be dialed.
While waiting to hear a response on whether this is a known issue, another peer (Steve) shared a few workarounds which I thought were quite good
1. Terminal.app command - open 'tel:+1425 <--finish typing a legitimate number
2. Want to type the + then switch to the Contacts tab
3. Want to use the phone tab then use the international digit string - 0111425 <-- finish typing a legitimate number
I would guess I didn't experience this earlier as I clicked on contact names and chose call or I was on the Contacts tab which worked.
TomL LCSKid with help