How to drive a speaker (earpiece) in an antique (vintage) phone (67 ohm)
An audio amplifier will in most cases (modern boring designs, not tubes or esoteric amplifier topologies) not be harmed or have any difficulty with a higher impedance than typical. The output is approximately a voltage source, so a higher load impedance means less current flows. No big deal (unless it's too quiet).

If you want to be sure that you're using an appropriately designed amplifier for the application, choose one intended for headphones — impedances on the order of 67 Ω are entirely normal for headphones. Headphone amplifiers are also designed to suit the application by having lower noise (since you're putting your ear right up to the speaker).