I didn't suggest to lie, I said, what if the customer actually doesn't have a mobile? Have we reached the point now where if someone claims not to have one, they're lying?

I should clarify i wasn't referring to myself - I have a mobile (deGoogled, at least). But there do exist people who don't want or need a mobile device.

You replied to “I forgot my phone” and I thought you were helping that argument.

No, wasn’t a lying argument. If you go out without your phone, fair answer to give.

sure, but you may still have a landline. but... the whole "we need this for returns" line is just weird.

exactly, just say no, firmly. most folks (retail or otherwise) would rather avoid confrontation so will opt for the workaround (that retailers institute as a backup since they typically would rather not lose business entirely).

but also, have no qualms about providing false information. you have no legal obligation in most cases to provide accurate info, and companies often employ deception in trying to elicit oversharing private info anyway.