Refurbished and used phones aren't the same. All refurbished phones are used at some phones. However, a used phone may also not be refurbished.
Refurbished phones are preowned devices that are repaired and tested to work as if they were new. Used phones may or may not have defects, which refurbished phones completely avoid.
You can buy used phones, but they do not come with a warranty unless you are buying before the warranty period is over. Refurbished phones have a warranty.
buying used phones comes with some risks. These phones are sold by private sellers who don't guarantee the phone's optimum condition. Only authorized and reputed sellers sell refurbished phones.
Both refurbished phones and used phones can be value for money if you check them well before buying them.