I don’t know what to do it has to deal with calls

So I didn’t really have a problem with this until the past 2-3 years and I want to see how to fix it but after 8hrs like on the dot it says call failed and I don’t even touch my phone and this really sucks cause I have to be on my phone longer then 8hrs for my job and it’s really stressful sometimes cause it could be an important call and I can’t get it back please let me know if you have any idea how to fix this