calls go right to voicemail instead of ringing

[Grammajo]

Only certain calls go right to voicemail like my doctor.

[vape]

sounds like you have his number blocked. also check and make sure you have do not disturb feature on

[Kinsley]

Hi Grammajo,

When you are talking to someone on the phone, or multiple lines are engaged this might happen and make sure Airplane mode is turned off.

also, check whether the number is in the block list and do not disturb mode is disabled as mentioned by @vape.  

You can try safe mode.  Sometimes a third-party app can change settings,  which might affect the calling feature.