Auto Increment after delete in MySQL

What you're trying to do sounds dangerous, as that's not the intended use of AUTO_INCREMENT.

If you really want to find the lowest unused key value, don't use AUTO_INCREMENT at all, and manage your keys manually. However, this is NOT a recommended practice.

Take a step back and ask "why you need to recycle key values?" Do unsigned INT (or BIGINT) not provide a large enough key space?

Are you really going to have more than 18,446,744,073,709,551,615 unique records over the course of your application's lifetime?

ALTER TABLE foo AUTO_INCREMENT=1

If you've deleted the most recent entries, that should set it to use the next lowest available one. As in, as long as there's no 19 already, deleting 16-18 will reset the autoincrement to use 16.

EDIT: I missed the bit about phpmyadmin. You can set it there, too. Go to the table screen, and click the operations tab. There's an AUTOINCREMENT field there that you can set to whatever you need manually.