Freebase Dali

You're using a phone. How low of a frequency do you think your phone's speakers are actually reproducing? Chances are, you're just dealing with lower mids acoustically, and not even the lowest ones. It's physically impossible for such small speakers to reproduce the low tones you may be looking for.

You might have better luck using a resonator, which would be a hollow box or object that will amplify the vibrations that are sympathetic to the lowest frequencies. For instance, if you picture a Kalimba, these have a resonator box built in so that the tines will create vibrations that reflect within the empty space confined by the shape and make of the box, just like an acoustic guitar.
Think about the design of ported subwoofer cabinets and go from there. While your phone's speakers will only be capable of reproducing frequencies in relation to its ability to travel back and forth at a particular frequency, which is directly proportional to the size of that speaker, you can still amplify what it is producing by allowing those waves to propagate through an environment that allows for waves to concentrate within a confined space for longer, versus just being shot off into the room and decaying before they have a chance to overlap.

Since you know that sound is simply vibration affecting air molecules at different rates of speed, and that hollow objects internally resonate vibrations sympathetically to its structure, you may be able to use that knowledge to do what you're trying to do.
However, you're dealing with SPL levels of a phone.
Honestly, I don't know why you just don't buy speakers for it.

__________________