Jmod only helps with some block chance. They do the same damage. But it is helpful to help you stay alive in some instances. Also, 20/20 monarch or jmod does way way more damage than Phoenix. You don't need Phoenix if you have mana leech on gloves and some maek. 2 java/20 ias/mana leech gloves and opalvein lightning ring with +3 maek is plenty enough to maintain your mana. If you're still struggling, you can use opalvein lightning +3 maek and mana leech str/dex/life rare rings.
Phoenix is a very cheap budget option to keep your mana up, but if you buy correct gear like I listed you don't have problems with mana. Your merc should be using infinity, not insight.
you are awesome and get my vote for most helpful reply. so i get a 10 fcr new ring with maek opal, i dont have mana leech on gloves currently have 3/20 gloves. have dual leech on a ring with fcr im using and i dont feel the mana leech. honestly i just took infinity off for an insight and it feels the same clear speed (im using spirit not phoenix) debating if its worth it to buy 4 facets and make a monarch?