Once you are connected with the agent simply state "I am wanting to see if I qualify for the iPhone XR 64 GB for $149 with a 2 year commitment"
If you are an AARP member or have an employer FAN the upgrade fee should be waived.
Optionally you can call AT&T and ask to speak to someone in the loyalty department and ask for the same deal but they do have high call volume for Christmas so you might be on hold for a bit.
You need to be on a current Unlimited plan or switch to one of the unlimited plans to get this offer which will result in the $40 line access fee. If you are already on an unlimited plan then your plan will not change but you can verify that with the AT&T rep.