make an appointment at Apple Store

you do not need an appointment to purchase something at an Apple store - only needed for tech support/Genius Bar.

Aside from that, we are all other users here and unable to make an appointment for you.

As babowa said they don't make appointments for purchases. When you get to the Apple Store check in with one of the people with the iPads at the front of the store and tell them you want to buy an iPhone. They will connect you with a salesperson.