Doomfletch's Prism Royal Bow - Path of Exile

Doomfletch's Prism Royal Bow

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Description

Doomfletch's Prism is a unique Royal Bow. Bows. Physical Damage: 14-56. Critical Strike Chance: 5%. Attacks per Second: 1.45. Requires Level 40, 95 Dex. (20–24)% increased Elemental Damage with Attack Skills Adds (12–16) to (20–24) Physical Damage (10–14)% increased Attack Speed 60% increased Mana Regeneration Rate Gain 100% of Weapon Physical Damage as Extra Damage of each Element Flavour Text: 'The Vaal, a thousand years ago, came up with more delightful methods of murder than I could ever wish for.' - Koralus Doomfletch

Could you confirm that the Doomfletch (and its fated version) mechanic "Gain 110% of Bow Physical Damage as Extra Damage" scales with flat added phys from other items?

Yes.

How does Increased Attack Damage (from something such as Crown of Eyes) work with The Goddess Unleashed and the new 'Fated' Doomfletch, specifically the mod: Add X% Bow/Sword as Y Element(s)? If it applies at the end of all the conversions, wouldn't that effectively make it a 'MORE' multiplier?But if it applies to the Physical and then the Fire, wouldn't the effect of Increased Attack Damage be doubled for the Fire and not for the Physical?

These are, as you've correctly noted, conversions. Converted damage (or converted anything) is the thing it's converted to, and is affected by modifiers to it, but it is also affected by modifiers to the thing it used to be. So the fire damage that was converted to physical is affected by increased fire damage, increased physical damage, and increased attack damage, and all of these stack additively, since they're increases.