It seems to me that we are conflating not two but three different things:

1. The global volume setting. Manatus and juiceme are right, doing that is silly as the device is already too loud as it is, and it can be dangerous for the hardware. Not just the speaker but possibly even for the amplifier.
2. The volume of the screen feedback, such as pull-down menus and key presses. There is no separate setting for the volume, only an on/off switch (Settings->Sounds and feedback->Touch screen tones). This is what I was referring to in my post when I asked how can increasing that volume be dangerous, not realizing that you were talking about #1 above.
   The best solution would be to ask Jolla or find where that feedback is played. Alternatively to find the file with the tone and edit it to increase the volume.
3. The term "haptic". As juiceme says, the term normally applies to the sense of touch. It has nothing to do with sound.