All smartphones today can save files for works without any problems. If you are a student, you should choose Samsung note with S pen which can help you in learning or writing, it is very convenient for work with a big screen too.
There are a few popular smartphone brands as iPhone, Samsung, Sony, Google smartphones...etc which brand will you want to choose?
Finding a smartphone that suits your needs is definitely a start, if you a need a large amount of internal data storage then you should find a one with the highest specification.
Having said that you also must see to it that your files are well secured and managed. A large amount of data storage will not accurately help you if you cant manage your files efficiently.
I suggest that you should also consider a great file manager along with the smartphone.
I suggest you should buy a mobile phone that has expandable memory so that can change memory every time your memory is full. Not like the mobile phone that has built-in memory were you are forced to delete files every time your mobile phone memory is full. Yes, there are virtual storage like iCloud but the question is would you like pay a money for an expensive extra storage? And not just you have to pay to iCloud, you also need internet connection to access your file in iCloud not like in the detachable memory card where you don't need internet to access a file.
Samsung Galaxy J7 Pro is the best for me!! With its great looks, strong blend of features and performance, and a reasonable price, the Galaxy J7 Pro (2017) has long been the darling of Samsung's lower-end lineup, and it's still one of the best deals Samsung has on the table. The Galaxy J7 Pro (2017) uses top quality components that don't compromise at all, and in the mid-range segment, it's more affordable than many rivals, yet has all the features that you need at the right price. I really love this phone!!! Must check and try..
I would not recommend that you save your files on any smartphone no matter what capacity it has. This is a disaster waiting to happen. Smartphones are machines and like with any machines are likely to crush. I would recommend you save your files on a Cloud like Google Drive or One Drive. In case your phone crushes you will still have your files.
Any kind of Smart Phone will do as long as it has 2GB Ram and a 16GB Internal Memory, it's better also if you choose a reliable brand and for better visuals buy a phone with a large screen atleast 5" minimum. When it comes to processor a 1.4 to 1.6Ghz Quadcore will do, it really depends on your budget.