The hard cap for evade is 50%, but you will never reach it on Phoenix.
You can reach it if a support class without weapon spec or a caster tries to melee hit you.
Even vs the lowest weaponskill classes you won't reach much over 35% tho because we have NF RAs = no dodger.
I play a pierce ns with a lot of aug dex and qui and rarely reach 30% evade.
(Your combined evadechance gets reduced by enemy weaponskill and weapontype, dual wield reduces it by 1/4
On Uthgard they ran a test about weaponskill, check https://www.uthgard.net/forum/viewtopic.php?f=15&t=17494 - however Phoenix might have different modifiers)