my phone says 'to enter a number, tap the area code first' what does this mean

Apple's Support Phone Number: 800-275-2273

The first three numbers (bolded) are the area code.

Q: my phone says 'to enter a number, tap the area code first' what does this mean

It means that when you dial a number, or enter it in your Contacts list, you must include the area code - so in the example given above, 800-275-2273, not just 275-2273.