The phrase directs takbir with each individual pebble. A useful memory pattern is to pair each action: throw 1 + takbir, throw 2 + takbir ... throw 7 + takbir.
This guards against mistakes in the count and in the placement of remembrance. Omitting a takbir and omitting an act of stoning are not automatically the same legal omission: the core rite and its accompanying remembrance must be distinguished.