“I am looking forward to working with you” is correct. In this case “to” is a preposition, and you always need to use the ing form(gerund) after a preposition. “I am looking forward to work you” is incorrect.
Welcome to the team, John.
Thank you, I am looking forward to working with you.
I am looking forward to working with you!
“I am looking forward to working with you” is a nice phrase that you can say to someone when they offer you a job and you accept. This could also be a reply when someone says “welcome aboard”.
The phrase “I am looking forward to working with you” shows that you are friendly and ready to start a working relationship with someone.
Let’s look a little bit into the grammar of why we use “working” and not “work” in this phrase.
“To look forward to” is a phrasal verb
To look forward to something is a multi-word phrasal verb.
A phrasal verb contains a verb and a preposition and in this case, two prepositions(forward and to)
I am looking forward to spending the summer by the beach.
To look forward to is a transitive verb which means that it needs an object( a noun or a pronoun).
Other examples of transitive verbs are like and enjoy. You can’t say “I like” without an object.
I like tennis.
I enjoy swimming in the sea.
Gerund after a preposition
There is a rule in English that says that if you use a verb after a preposition, then the verb needs to be in the ing form(gerund).
Thank you for buying me breakfast.
He always dreamed of going west.
After working with the doctor, I went home.
“To look forward to” is a phrasal verb, so “to” is a preposition in this case. Try to remember that “look forward to” is always together and a set phrase.
More phrasal verb examples(Notice the ing form after the phrasal verb)
He started out cleaning the toilets.
John ended up renting an apartment next to me.
Different uses of to
The confusion between the difference between “I’m looking forward to work with you” and “I am looking forward to working with you” is because of the word “to”
After many verbs, it is necessary to use the infinitive(to + verb) or the gerund form(ing) of the verb for the second verb.
As explained above “to look forward to” is always together. It can’t be separated.
Examples of infinitives
I want to go to the supermarket
I tried to open the bottle.
Examples of gerunds
He likes swimming in the sea.
He enjoys dancing by himself.
“To look forward to” is an example of a verb that takes a gerund.
I am looking forward to seeing you later.
I am looking forward to taking off my shoes.
I am looking forward to playing my guitar later.
I am looking forward to meeting your family.