How are you calibrating your desktop monitor?
I don't think I have. Can you tell me how please? Thank you so much
This likely is a problem with calibration on your desktop. Most likely a corrupt display color profile. You need to use a hardware calibrator such as a spyder Pro, a colormunki, eye1 etc. these are essential tools. If you don't have any of these, you should set the display profile to sRGB. You are likely on a windows machine if you have this issue and you do this change by going to the monitor properties and deleting the color profile associated with the monitor.
That said, you should first make sure you turn off any of the night shift features on the phone. They shift colors unacceptably and can make your phone' colors look really bad in indoor lighting or late at night.
Ideally, you need a device like the Spyder to get the colors correct.
You can eye-ball the brightness and contrast using this file.
Adjust the screen contrast to see the difference between ABC.
Adjust the brightness to see the differences between XYZ.
Most people have their screens set WAY too bright.
When exporting your images for the web or for other devices, sRGB is the correct color space to use.