Calibrum has two passives. As the game details, one passive applies to attacks within abilities and the other passive applies to attacks outside of abilities (when the weapon is equipped). Weapon passives are only applied to attack from that specific weapon.

If Calibrum only had a single passive then either it would be the mark and it would also apply to every basic attack which would be far too powerful or it'd be the +100 range and it would apply to attacks within abilities which wouldn't synergise with Infernum's Q, which has a predefine range for its follow-up attack, nor Aphelios' R, which only adopts an on-hit effect.

Infernum's Q is a two part attack which first does a sweeping attack with Infernum and then a follow-up attack with your off-hand weapon on the targets previously hit. Only the follow-up attack would be affected by a range increase passive and +100 range wouldn't do anything since the targets for this attack are already defined. It also wouldn't work with your ultimate which only applies an on-hit effect based on your currently equipped weapon. In this case an exception would need to be made for Calibrum.

Ignoring all of this, it's likely a deliberate decision for the range of his abilities to be consistent. Aphelios is quite a complicated champion and having all his abilities periodically shift between two different ranges wouldn't only serve to further complicate him and make him all the more harder to predict.