My simplified combat system

I like to run combat as easily as possible. I don't like systems that are heavy on rules; rather, I like this combat system because it's great with novice and/or impatient players.

You should optimally use 6d6 for this combat system. 3d6 is fine too. It's based on the dice game Cee-Lo.

Phase 1 - Determine Attack
the attacker decides what kind of attack or skill to use.
the opponent decides what kind of defense or skill to use (if applicable).

Phase 2 - Determine Advantage
The attacker begins with advantage
If the opponent is wounded, incapacitated, or can't defend, automatically skip to phase 3
If the opponent isn't wounded, incapacitated, and can defend, they have a chance to flip the advantage.
The attacker rolls for advantage:
1.    roll a d20 + either STR mod or DEX mod against the opponent's AC for melee attacks
2.    roll a d20 + INT mod against the opponent's specified defense for a spell
3.    roll a d20 + appropriate mod against the opponent's specified attribute for a skill
The opponent rolls a d20.
If the opponent rolls higher than the attacker, the advantage is flipped.
If the attacker and opponent roll the same number, they must win only one dice round each.

Phase 3 - Dice
The attacker and opponent both roll a 3d6. If a pair is rolled, the third number counts.
Whomever’s roll turns up a higher third die with a pair wins the round.
The character with advantage must win 1 round first; the character without must win 2 first.
a 456 wins the phase
a 123 loses the phase
a 666 wins with a critical hit
a 111 loses with a critical miss
any other triple (like 333) resets the win count;
any other phase-ending roll trumps this
two identical rolls up the required wins by 1 for each combatant

Phase 4 - Assign Damage
Roll for damage.  Check for appropriate modifiers.