Trying to enlarge tiny fiberglass shower stall so we can roll wheelchair into it (no lip). It will be tile. Contractor came to give an estimate & says that he will need to remove part of the foundation to create the slope to the drain. Is that correct? He also wants to use small tiles on the floor as they are easier to install to create the slope to the drain. Right?

Agree on both counts. Your fiberglass shower probably has a sloped pan and a permanent pan will need to be installed. Very large floor tiles are hard to "tilt" to get a slope.