Contact details are not asked for until step 5
The phone number comes after the price and after a slot is already held. Everyone who leaves before that is unreachable.
Why we suggest this
Most of the hesitation in a booking lives in the schedule and price screens, and today both of those come before we have captured a single contact detail. Anyone who hesitates there leaves as an anonymous visit.
The changeAsk for a name and one contact field right after the treatment choice, before any price appears.