We have couple of Ubuntu based instances running Php. Then on developer side we have almost same type instance. So if on server we use php 5.6 and mysql 5.5.4 on 14.04 Ubuntu LTS then we use the same on Developer Side. As of now all of our instances run on 14.04 LTS. The only packages that concern us are related to LAMP. Question is if we choose to upgrade to new version will it mean that our LAMP stack packages could be different from fully updated LTS version?
As long as all your computers are running the same version of Ubuntu (14.04) with the same repositories they will have the same packages available to you when you update (upgrade).
Updates, for the most part, contain security patches and bug fixes. Sometimes a packages update will contain a newer version, but, in general, the backport repository or a ppa would be used for more recent or higher versions of packages.
What to expect from an update is outlined here - https://help.ubuntu.com/community/UbuntuUpdates
You may of course elect to do security only updates - How can I install just security updates from the command line?
If you need a newer package that is not in the repos or a ppa you would have to search for a .deb / repository (check the project home page), build from source, or upgrade to a higher version of Ubuntu.
Generally speaking, server side, most people prefer long term releases (such as Ubuntu LTS, Centos, RHEL) for stability at the sacrifice of newer packages and newer feature.
With that general overview, what is it you are wanting ? security only updates ? A package not in the repositories ? Please update your question if this does not answer what you are asking.