NinjaTrader's fees are listed on their website at the following link: https://ninjatrader.com/Admin-Fees
You'll notice that some fees vary by broker. If you see a fee on your account at Phillips or Dorman, it may not be them assessing the fee - they are just processing the fees charged by NinjaTrader.
Note that NinjaTrader requires that a round-trip trade be placed at least monthly to avoid an inactivity fee if you log into the system in that month. This is known as the "Minimum Activity Fee", and is listed at the linked webpage, above.