Putting my phone in low power mode can it destroy the battery

I don't think so.

To turn Low Power Mode on or off, go to Settings > Battery. You can also turn Low Power Mode on and off from Control Center. Go to Settings > Control Center > Customize Controls, then select Low Power Mode to add it to Control Center.

Use Low Power Mode to save battery life on your iPhone or iPad

I do not feel it destroys the iPhone battery, I personally have been using it effectively for over a decade. it is meant to make your iPhone last longer, and every feature iPhone has a way to be used. They are for enhanced usage.

To Use low power mode, go to Settings > Battery. Another way to turn Low Power Mode on and off is through Control Center. Go to Settings > Control Center > Customize Controls, then select Low Power Mode to add it to Control Center. And whenever you want to use it you can do it directly from there.