Updating 2009 Macbook Pro Software

I have a 2009 Macbook Pro. My latest update is 10.10.5 and it is not showing any more updates in the app store or in system preferences, but when I connect my phone to my computer it tells me that I need to have 10.11 or later in order to connect my device. How can I get the latest update, or is that even possible with my older model macbook?