Thanks for contacting TextNow Support!
Your battery can warm up if your phone is using a lot of power - downloading a lot of updates, for example, or playing a game that requires a lot of processing power. You can see what specific apps and services are drawing the most amount of power under your main Settings app > Battery, and that page will also have options for battery-saver settings.
If it's getting too hot to touch, that might be a problem with the battery itself. If that's the case, please contact us at TextNow Support at 1-888-250-5255 and we can go over some troubleshooting steps and options for replacement.
Our Support department is open Mon-Fri 9am-10pm, and Sat-Sun 9am-5pm Eastern Standard Time.