While trying to install my iOS 15.7 version on my phone

Thanks for posting the screen shot.

You will need to be connected to a Wi-Fi Network AND your iPhone must be charged over 50% to download and install the update. The other requirements are listed below:

Make sure that your iPhone is setup to meet the following requirements before you attempt to update the iOS version over a Wi-Fi Network. Open Settings ➡️ General ➡️ Software Update: If there is an update available for your iPhone then it will be listed here. Follow the on-screen instructions to download and update your iPhone. 

• Your iPhone must have a fast Wi-Fi connection; you cannot update over cellular data or a cellular hotspot
• The iPhone can not be in Low Power mode
• The battery state of charge must be above 50%
• Your iPhone must have at least 6GB or more free storage space
• Your iPhone cannot be connected through VPN
• You should leave the phone plugged in until it finishes updating, both to assure that it remains above 50% and to keep Wi-Fi enabled (Wi-Fi turns off when the phone sleeps if not connected to power).

Axel F.

You cannot use Hotspot during this process.

If your iPhone or iPad won't update - Apple Support

Connect to a WiFi network. A hotspot connection will not work.

Leave the phone connected to the charge circuit.

Attempt the update again.

As stated, a hotspot connection from another device will not work. You must use a wifi connection.