Is showing off worldly things like showing off wearing nice clothes or showing off your new phone and seeking validation from people is this haram.

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

A person is not blamed for his love of wearing beautiful clothes and his love of owning beautiful, permissible things. It was said to the Prophet “What if a man likes his clothes to look good and his shoes to look good?” He said, “Allah is beautiful and loves beauty.” [Muslim]

As for showing off and bragging about the blessings of Allah upon people, then this is reprehensible in Sharee’ah. The commentators said that "competition" in the words of Allah the Almighty, {Competition for more gains diverts you from Allah, until you visit the graves (i.e. till you die.)} [Quran 102: 1-2] means “you were preoccupied with showing off and boasting about what you piled up of worldly things until you remembered the people of the graves.”

Allah Almighty also says in His book (what means): {Allah does not like those who are self-deluding and boastful.} [Quran 4:36] Commenting on this, Ibn Jareer said: “As for Al-Fakhour (the boaster): He is the one who boasts to the servants of Allah for what Allah has bestowed upon him of His bounties.”

Scholars interpreted “libaas ush-shuhrah” (lit. dress of high repute, the garment of fame) which is forbidden to be worn according to Sharee'ah, as what is worn to show off and boast to others. A hadeeth reported by Ibn Maajah and others states: “He who wears libaas ush-shuhra, Allah will clothe him in a similar garment on the Day of Resurrection...”

Al-Minawi said in Fayd al-Qadeer: Because he dressed it to show off to others.

The honorable companion Al-Nu’man Ibn Basheer described pride and boasting about the blessings of Allah Almighty as a trap by which Satan traps people. In al-Adab al-Mufrad by al-Bukhari, with its transmission classified Hassan by Al-Albani, on the authority of al-Nu’man ibn Basheer that he said on the pulpit:

“Satan has snares and traps. The snares and traps of Satan are to exult ungratefully in the blessings of Allah, to boast about the gifts of Allah, to have pride over the servants of Allah, and to follow desire for other than the sake of Allah.”

Ibn Rajab al-Hanbali said in Jaami’ al-‘Ulum wa’l-Hikam in an explanation of the hadeeth, “and when you see the barefoot, the naked compete in constructing tall buildings.” In his saying: “they compete in constructing tall buildings” is evidence of the condemnation of showing off and boasting. End of quote.

As for striving to please people, if it is by doing something forbidden, then it is not permissible, such as one who commits a forbidden act to please them. A hadeeth states, "...whoever seeks to please people with something displeasing to Allah, then Allah and the people will both be displeased with him.” [Ibn Hibban]

As for pleasing them with something permissible, then there is nothing wrong with it, such as someone who pleases his relatives, neighbors, or friends. The basic principle is that this is permissible.

Allah knows best.