Flight number - look online and find a flight 2 weeks after when you’ll apply for the visa and use that flight number. I held a flight with BestOnwardTravel.com for 14 days while I applied for my visa and included the confirmation pdf in my application. Some people don’t do this and just find a fight number.

Accommodation - book somewhere with free cancellation and use that hotel name and address and include the confirmation pdf in your application. You could also not book and just find any accommodation name but I didn’t risk that.

Phone number - I don’t remember it specifying Thai number, if it’s in travel section, it’s the Thai phone number for the accommodation. For your phone number, this is in the current or permanent address section.

My application from Hanoi: