新

Chinese adjectives squeeze tight against short everyday nouns, so 的 falls off. 新朋友, 新书, 新手机 are what people actually say in a group chat or a coffee shop. 新的朋友 is not broken Chinese, but it sounds like you are spotlighting 'the friend who is new'. Save 的 for contrast, as in 我要新的，不要旧的。 Rule of thumb: one-syllable adjective plus short noun, drop the 的. “新朋友，叫什么？” (A new friend — what's their name?) ── [《问问题》](/read/asking-questions-daily-life#s12)

Adjectives can't carry a whole sentence in Chinese; they need a little ballast in front. 我手机新 sounds cut off mid-thought, while 我手机很新 lands normally. In that slot 很 stopped meaning 'very' a long time ago. It is the grammar holding the sentence upright. Want real emphasis? Stress the syllable, or say 特别新, 超级新.

新 doesn't only mean 'brand new out of the box'; it also means 'recently' when it sits on a verb. 新买的手机 is the phone you just bought, even if it's an old model. 新来的老师 is the teacher who just showed up at your school. You'll hear this all day at the office: 新来的, 新买的, 新做的. Just never put 的 between 新 and the verb.