Can I use the credit in my itunes account toward the purchase of a new Iphone?

You can use the gift card credit to pay for iCloud yes. And you can use it to pay for Netflix if its being billed through iTunes.

Any charge through iTunes will use any available gift card credit balance on your Apple ID.

If your Netflix account is being billed directly through the Netflix website, or another platform you will not be able to use that credit to pay for it.

No. iTunes credit can only be used to purchase items from the iTunes, iBooks or App stores.