We were unable to squeeze an executive briefcase in.
I carried my briefcase with me through the airport.
The lawyer opened his briefcase.The thief ran away with my briefcase.
It is almost correct: it simply needs an article before the word phone, to make the sentence "Yours is the briefcase with the phone ringing inside." This sentence could be the answer to the question, "Which briefcase is mine?""The briefcase with the phone ringing inside is yours" is a more common construction, however.
These briefcase are also for men.
If this is your briefcase, you're going to have to move it.
That is the lawyers briefcase.
"Lost" is a past-tense verb.
Yes, and if anyone argues you're ending a sentence with a preposition, they're wrong. In this case, 'inside' functions as an adverb answering the question "where is the phone ringing?" The possessive pronoun 'yours' is correctly taking the place of the noun briefcase as the subject of the sentence. The object of the linking verb 'is' is the complete noun clause 'the briefcase with the phone ringing inside'.
The barrister did not have all the information, because he had left his briefcase in the office.
Briefcase is a noun.
The possessive form of the singular noun briefcase is briefcase's.example: My briefcase's strap is broken.
The plural of briefcase is briefcases