If you have any old cassette tape lying unused in the house, you can use the plastic case of that cassette as a desk stand for your mobile phones. Just remove the cassette tape, open the case upside down and insert your phone as shown in this video.
The mobile phones may either be placed in portrait or landscape mode.
I have an Android phone where the speaker is located at the back of the phone. If I put that phone on the desk, the music is barely audible but when I put it vertically inside this simple cassette stand, the problem is solved. The desk stand is also handy when you are watching a movie on the phone while working on the desktop. ↓