Is this a recent thing?
I get spam calls sometimes, not multiple times a week though, and usually I just ignore them when I'm with DP. BUT, I will usually say to him i'm not answering that its a sales/spam call or something and he likely could clearly see the number on the screen anyway.
So the key here, is he secretive about it? Does he reject it very quickly?
Only reason I say that is because when I get them it takes me a second or 2 after seeing the number to think, who is that? and then think, well I don't know anyone from liverpool, so then I reject it. Spam calls rarely come in from the same number. Rejection isn't instant, proabably a few seconds whilst my brain works out if I recognise the number or not.
If hes seeing it and instantly rejecting it, it would suggest he knows the number straight away and doesn't want to take the call.
Does that make sense?
Can you check the calls list on his phone to see if they are spam numbers?
If its suddenly started out of the blue, I'd be getting a bit suspicious. But it really depends on lots of factors. Does he use the phone for work? recently signed up to stuff that may have shared his number etc etc
My DP for example, literally never gives his number out and doesn't use it for work. he gets zero spam calls. If he started doing this multiple times, i'd definitely think something was up.