Collar or no collar?

When we picked our basset up from the breeders she told us to never put a collar on him as it can hurt his neck(we have always used a harness when walking him ), however, we do put a collar on him too when he is on walks incase he somehow slips his harness as it has our phone numbers on it (he’s also microchipped so this is just for extra safety), so this is just to ask if it is okay to use put a collar on their necks?

Thanks!