Are electric linear solenoids the best option to push a capacitive screen button on a smartphone?
A capacity touch screen really needs no force at all, so these kind of actuators are all horribly overpowered.

In fact, capacitive touchscreen actually do what their name says: measure the capacity between screen matrix and ground. When you put your finger on a screen, it forms a capacitor.

So you don't have to build a mechanical actuator at all. You just have to vary capacitance at the places you want.

I call this prototype that took me nearly 5 minutes to build A.W.E.S.O.M.E. (Advanced Wire-based Electrical Sensory Obfuscator Manufactured from Edibles). I made it from high-tech potato slices, and bits of wire.

ECG pads, which are cheap and can be bought in hundreds, together with ECG contact gel, which is cheap and can be bought in bottles, probably work just as well, but I had neither of these at hand. As little as I had access to conductive sticky tape or conductive glue that I wanted to put on my phone's screen.

So: here is A.W.E.S.O.M.E., with none of the V.I.C.E.s (Vegetable Interface Contact Entities) grounded:



and here with the croco clip connect to my heating pipe:



So, use short leads with no ground plane near, and a set of transistors with a high "off" resistance, and you should probably be able to build your touchscreen toucher without any mechanical actuator.

So, no, I personally don't believe that solenoid linear actuators are the most awesome way to interact with your phone screen.