Either your area has recently started requiring all calls use the full ten digits of the phone number or you are close to another area code location where there is some overlap now. Either way, you should always dial the full ten digits of the phone number when dialing from a cell phone. When I got my first cell phone twenty years ago or so, I was told to always dial the full ten digits of any phone number on the cell phone even if the area I was in didn't require all ten digits for the call to be connected when you dialed the same number from a landline.
I'm most definitely NOT a VZW employee. If a post answered your question, please mark it as the answer.