Duplicate contact on my iphone

Assuming these are iCloud contacts, the easiest way is to use a Mac if you have one (the article explains how to do that). But you may find that there's one more step, because (at least for me) removing the duplicates on my computer didn't get rid of the ones on my phone.

For that I would suggest - after you've merged the duplicate contacts on your computer - going into your phone iCloud settings, turning off Contacts (say yes to deleting them from your phone), wait a minute or two, and then turn Contacts back on in iCloud. It'll take a few minutes to sync back up, but the duplicates will be gone.

Read and follow the article linked above.