To follow up on the above while it is possible to use your iPhone as a "stand alone" device it is not ideally suitable for reviewing, editing and managing a large online library of photos due to its limited storage and small screen.
Perhaps I should explain how my system works, I apologise if you are already familiar with this but of course we have no way of knowing your level of computer knowledge:
I take a series of photos on my iPhone.
I do not use iCloud Photo Library but I do use iCloud's My Photo Streaming service. This means all photos I take are synced to my MBP for 30 days where I can review and or save them to the photo library on my MBP.
I can also simply connect my iPhone via USB cable (like a camera) and download all of the contents of my Camera Roll to Photos on my MBP where they are added to my library, I get the option to delete them from the iPhone at the same time.
My MBP is backed up to 2 External USB Hard Drives.
This is the way Apple has designed the system to work although no doubt they would prefer me to use iCloud Photo Library as well, not to mention Desktop an Document storage and a whole host of other information. I am resistant to using any more iCloud storage than I absolutely need to sync things like contacts, calendars, notes and reminders so that my wife and I share just 50Gb of iCloud storage only. I do backup my iPhone however because I am an overseas traveller.
So upgrading your MBP to El Capitan would give you a later iPhoto and some other transfer options not to mention iCloud access but, and this is an important consideration, if you are running the original Hard Drive in your MBP, rewriting it as part of an Operating System upgrade could cause it to crash. The average life span of a HDD is only about 5 years. One of our members has a footnote which states "it is not a matter of if your computer will crash but when".
In an ideal world I would simply advise you to purchase a new or refurbished MBP which would give you all of the afore mentioned features, options and resources as well as improving your online security but I do not know your financial situation or options in that regard.