Activate iPhone 6 to use as iPod

An iPad cannot be used to restore/activate/update an iPhone. You do not need a computer to Activate or update an iPhone, although you can use on, but you do not need it. You will need a computer if the iPhone has been disabled.

What is the current status of your iPhone 6? How do you want to see it working for you?

Axel F.

Not to set it up, no, and you don't even need a SIM card. Just set it up via Wi-Fi as Apple describes here.

If you are intending to use it as a music device you will have to put content on it, perhaps from an Apple Music subscription? If you want to move your own music to it from iTunes or the more recent Music app you will need a computer to achieve that.