The amount of time one spends on their mobile phone daily varies greatly from person to person. Some may use it for just a few minutes, while others could be on it for hours. Here are a few phrases in English that can be used to describe different phone usage times:
A few minutes a day: I only spend a few minutes on my phone each day.
Around an hour a day: I use my phone for about an hour every day.
Several hours a day: I'm on my phone for several hours every day.
All day long: I'm constantly on my phone throughout the day.
If you're asked how long you spend on your phone daily, you can simply answer with one of the above phrases based on your actual usage time.