Currently, the iPhone 14 Pro and iPhone 14 Pro Max offer a 3x zoom lens, and up to 15x hybrid zoom. So a variable lens may not offer the rumored iPhone 15 Pro Max a higher zoom level (Revegnus says they don't know what magnifications this lens would offer), but what it would in theory offer is a choice of optical zoom levels.
Variable lenses use moving parts within to allow for multiple magnifications without needing to crop pixels (as the current Pro iPhones do) or having to use a separate camera, like the Samsung Galaxy S23 Ultra does with its 3x and 10x dual telephotos. This is a relatively rare feature, appearing for the first time in 2021 on the Sony Xperia 1 III's 3x and 5x zoom telephoto camera. However, this is not the same as a continuous telephoto camera, such as the one seen on the Sony Xperia 1 IV, which can zoom at any magnification between its two extremes.
Even if it isn't continuous, having a choice of zoom levels would be of great benefit to iPhone users who want to take a greater variety of zoom photos without needing to sacrifice photo resolution. However, based on the wording of Revegnus' tweet, it sounds like the iPhone 15 Pro may not have this tipped adjustable zoom feature, something that would mesh nicely with previous rumors about the Pro and Pro Max's different camera loadouts.
How likely is an iPhone 15 Pro Max with variable zoom?
In some ways, it's hard to accept Apple would introduce such a radical change to the iPhone 15 series without other rumormongers having picked up on it.
Revengus is a relatively new leaker, but one behind several other big recent claims, such as that the Galaxy S24 Ultra will get a similar feature next year. He adds that sensors on the iPhone 15 Pro Max will apparently be the same 48MP/12MP/12MP combination as the iPhone 14 Pro, which at least sounds reasonable, even as the iPhone variable zoom claim comes straight out of left field.
We won't know for sure until Apple actually shows off the iPhone 15 series, which should be in September as usual. While a variable zoom lens sounds unlikely, we've heard rumors for other features, such as USB-C ports and solid-state buttons, that we would never have seen on previous iPhones. So perhaps it's not unreasonable to believe this rumor after all.