Welcome!
The Phals are shade plants. They do better with no sun ever on their leaves. They would probably be fine on your kitchen counter near the window, but not in the sun. You can use the sunny spot for more sun-loving orchids, like Cattleyas. There is a great thread here for learning to grow Phals:
The Phal abuse ends here.
Gnats might mean your potting mix is getting old. Most orchids in bark should be repotted every 2-3 years. Many Oncidiums are sold in sphagnum moss, which usually needs to be changed every year. If you haven't repotted for a while, now would be the time. The Phal thread above discusses it well. If you go to the Oncidium forum, accessible via the left yellow menu, you will find threads dealing with repotting Oncidiums. People grow them successfully in sphagnum moss, bark, and bark mixes. The medium doesn't matter; learning how to water does matter.
I know people who spray their house plant's soil with pet flea and tick spray to kill fungus gnats. You can also put a small fan blowing on the plants. The gnats can't fly against the fan, so they can't get back to the soil to lay their eggs. After all the larvae mature you will be free of fungus gnats. Your plants will probably need more frequent watering with a fan on them all the time.