There are plenty of sketching and drawing apps that you can download onto your Mobile Phone. Most of these are free, so you could download several to find one that you prefer.
Nearly all apps will have similar features. A few favourites are: "Ultimate Painter" on GooglePlay and "Drawing Painting" on App Store but there are many more.
Remember, it's what you do with it that counts!

Not used to downloading apps?
Look for "Play Store", "App Store" (or similar) icon on your phone. Follow instructions to get a list of all Apps available. Search for a "drawing" or "painting" App.

You might also have a simple drawing facility on the texting part of your phone. Simply sketch your image, and send the text message with the image attached, to yourself. Save the image to your picture gallery when you receive the text.