Nextcloud

Nextcloud is a FOSS self hosted dropbox. Why use nextcloud? Because you want to backup files. Things like emails, contacts, texts, all can and will be lost on a mobile phone if you don't have a backup. Nextcloud can sync these up.

Setting up Nextcloud

You can do a self hosted server and manage it yourself, but then you have to manage updates. Another option is to purchase hosted and managed nextcloud services. There is a list on the official website. This is the way to go, I think. Especially, if you are an IT guy and deploying this for multiple customers. If it's just you, then go ahead, use an RPI and host it from your garage / basement.