If I want to install the update is it necessary to backup all my apps and videos and photos on my phone
Updating of my iPhone
Updating of my iPhone
Almost certainly not but it is a wise precaution in the unlikely event that something goes wrong with the update.
Yes, it is recommended.
You should really be backing it up on a regular basis no matter what.
Why is it recommended
Would I lose all my datas on my phone if I refuse to backup before installing the update
If I want to install the update is it necessary to backup all my apps and videos and photos on my phone