iPhone call fails when moving away from ear after 18.0 update

All the out going calls are being connected successfully but during call if phone is moved away from ear the call is being disconnected and showing message “call failed”

This call fail is happening only when phone is moving away from ear i.e. when the display blanks out when phone is kept near ear during call and same display turns back when phone is moved away from ear the call and s being failed

but when call is being done in Loud speaker there is NO call fail

this problem started only after 18.0 update software has been installed

this is purely not the network issue

completely software issue

need to be resolved ASAP

[Re-Titled by Moderator]