How to delete duplicate contacts on iPhone 5?

Hi

While trying to import contacts from windows / outlook etc to iPhone I seem to have duplicated contacts

So I have something like this

Name.................Phone#
-----------------------------
subu's dad...........1234567890
subu's dad1.........1234567890
subu's dad2.........1234567890
...and so on

so you would notice that the phone #s are the same but the identifying name is different

I wish to retain one entry here and delete the rest

How do I delete duplicates without loosing original data ?

thanks in advance for all your answers