My phone abroad

Basically my current phone 8 plus is going to have the SIM card removed while I’m abroad and put in my old phone For my business to revive my calls so I will have a pay as you go sim in my 8 plus while I’m abroad now will my cellular Apple Watch switch to my contract SIM card that was in my 8 plus or the pay As you go or will it just stay with the contract sim without it being in the 8 plus.