When it comes to having additional support or resources at your disposal, there are plenty of synonyms for the phrase "more back-up". Some of these include "additional help", "extra assistance", "added support", "backup resources", "supplementary aid", and "further reinforcements". Other potential synonyms could include "additional resources", "extra manpower", "supplemental resources", and "added backup". Ultimately, the specific synonym or phrase that you use will depend on the context of your situation and what type of support you are seeking. However, having a wide range of options to choose from can help you communicate your needs more effectively to others.