I mean, I knew how a rotary dial worked (from a UX perspective) just through watching films before I ever got to handle one (and I've never placed a real call with one), so I'd assume that gen Z and A can still recognise a ye olde phone, assuming its not one with some wild design that's on the edge of the (Graham) bell curve of what constitutes a normal 'phone' shape.

Even then, most call icons I've seen don't only have the receiver as part of the icon, but some waves to, to indicate sound (speaker/sound icons often do the same, unless intend to mean 'mute', but that's usually paired with a cross or something). Given that, you could probably get away with anything half-moon-ish shaped, so long as it also has those waves on the upper end of the icon, and it'd still be recognisable as a phone receiver and a 'call' icon (please don't do that though. Just make a normal icon).