Is minecraft on iphone have the full version ?

Yes it does and it is only $6.99

Since the Better Together update, the mobile versions of Minecraft (formerly known as "Portable Edition") are running on the Bedrock Engine & is considered the Full Version of the game (that can be played with XBox One, Windows 10 & Switch users locally & online).

The only thing that costs extra would be optional content (Skins, Textures, World Templates, ect.) & Realm subscriptions. As for world size, it's officially "infinite", but the logical storage limit for everything (worlds, skins, textures, ect.) is 2 GB's... so could have a 100 square KM (10,000 x 10,000 blocks) world (taking around 1.25 GB's at last check) or possibly larger is you only wanted one world. If you like to have multiple worlds, the size of the world would likely be smaller to fit within the storage limit.

Please be aware that you'll need to have a Microsoft / XBox Live account for online support & the Minecraft storefront (utilizing "Minecraft Coins", which can be purchased through Apple's iTunes store).