You can use your smartphone to watch it, but only if it has a front camera. Use the front camera, and turn your back to the sun. You can then safely watch the sun on your screen and can even record it for viewing pleasure again and again. Do not use the rear / main camera on your phone unless you are wearing solar glasses, while the camera doesn't have retinas that could be damaged by the Sun's rays, your eyes still could be as you'll be facing towards the Sun to take any pictures / videos.
Sorry if you actually are interested in making some sort of glasses, but this tip might help some people.
