On my Galaxy Note 4, when I launch the phone and contacts apps, they say "Unfortunately, Phone has stopped" or likewise for "Contacts". I have to go through message program to make a call. What's the problem and how can I fix it?
From your comments on your post I can understand that your phone's system apps are crashing.I am going to list out some steps by which you might solve your problem.I have faced this kind of problems a lot and these are generally faced by users how are using a low end phone or a high end phone which has been used for many years.
The steps to troubleshoot your phone are:
1)Try restarting your phone.Sometimes the cache files(temporary files) takes up a bit of your storage.Restarting your phone helps in removing those useless files.
2)Stop temporary background processes which are neither used by the system nor by any of your third part apps which you generally use as they eat up your ram and the app you want to open does not get enough available memory which may be the cause of your phone and message apps getting crashed.
3)If the above steps don't work,take a backup of your important files and try doing a factory reset.
If the problem still persists feel free to comment down below.