Is "My phone is my lifeline to the world" a metaphor

Yes

Explanation:

Simile is a way to compare using like or as while metaphors compare things without using like or as

often a noun phrase is just a noun or a pronoun:

people like to have money.

i am tired.

it is getting late.

comfortable

explanation:

one type of the adjectives is predicate adjective. a predicate adjective is an adjective which follows a linking verb and modifies or refers back to the main subject of that linking verb.

it usually is used just before the noun it modies.

here in this example:

'penguins seem comfortable in the coolest habitats', comfortable is the predicate adjective which follows the linking verb 'seem' and modifies the noun.