Here is an eco-tip courtesy of Which? magazine. Their very useful article gives detailed information on how to recycle your mobile phone:
https://www.which.co.uk/news/article/how-to-recycle-your-mobile-phone-a4RH90q3yNtT
For more recent phones, you may be able to sell them so that someone else can use them again. For older phones, there are charities that will pass them on to people who need them, or sell them on to provide funds for the charity.
Every mobile phone re-used reduces toxic waste too!
The Which? article includes important information on how to make sure your data is not at risk if you recycle your phone.