"Where is the phone?"
Translation:¿Dónde está el teléfono?
https://www.youtube.com/watch?v=lY10_T_ROq4 You use estar for temporary things, location, positions and while doing an action. You use ser to describe attributes, to characterize, your occupation, to tell the time, to tell your place of origin/nationality and describe relationships.
Esté is used in subjunctive cases (when speaking in hypotheticals, about things that aren't actually happening or will happen).
You always use some form of the verb “estar” to talk about the location of an object. Está is the form you use to talk about one object or person. (Third person singular).
Why is it 'el' and not 'la'? Esta is for a girl, so it should be la I guess.
Spanish words have an assigned gender. Telefono is a masculine word so you use el.