I only occasionally have volume issues when in a noisy vehicle or location. In such situations, if I can't hear, I turn it on speakerphone on the lowest volume. The lowest volume speakerphone is louder than the highest volume standard speaker. I just flip the phone around so the speaker is by my ear and the screen is away from my face. A bit odd, but works.
(if anything, that borderlines on being too loud, but that's as low as the speakerphone will go...)
