When you make an Intelligence (Arcana) check to control a sphere of annihilation while you are holding this talisman, you double your proficiency bonus on the check. In addition, when you start your turn with control over a sphere of annihilation, you can use an action to levitate it 10 feet plus a number of additional feet equal to 10 × your Intelligence modifier.
RollQuest ships the D&D 2014 SRD as a content pack, on a 5e character sheet that does the maths - roll from the sheet and let the numbers work themselves out. Free to start.