In my games, there are usually several potions of the same type poured into one larger phiole, making a phiole a potion with say 4 charges.
But increasing the effect by drinking more than one dose is interesting. Maybe extending the effect like the potions caster level would be 2 higher for every additional dose taken. (Which is usually is not as effective as drinking the second dose after the first one expired, so it's less likely to break the game.)