I've had a couple of calls recently asking whether I can give a price over the phone and in each case I have said that I need to see the floor etc before I can give an estimate. In both cases I also had to mention that I would not be able to start for 6 weeks, so both enquiries said they would contact another
tiler - not really bothered but certainly wouldn't give a quote without looking at the job.
If the customer wants a price over the phone, they're probably not serious about getting the work done anyway - surely they would want to meet the potential tradesman face to face to establish whether they trust him/her or not, and want to use them?