1. "The radiation emitted from phones that operates in different environments...." 2. "The radiation emitted from phones that operate in different environments...." 3. "The radiation emitted from phones which operate in different environments...." Which one is the best sounding sentence?
You have a choice. You can use 'that' or 'which (without a comma)'. Personally, I prefer 'which'. This subject is covered is this lesson on 'that or which'.
Oh, provided you're talking about phones and not radiation, it's 'operate' not 'operates'.