Hello and welcome to Android Forums, Rosco.
I'm wondering if the proximity sensor is obscured by dirt or grease, etc and thus not allowing the screen to know it's not up by your ear when it's being held in front of you for viewing.
Clean off the upper area of the screen where the sensor is, using a soft dry cloth or dry cotton, etc, then have somebody test call you.
If that does not remedy the issue, perhaps a factory data reset could help.