電話がかかってるよ。

telephone call; phone call; telephone (device); phone

indicates sentence subject (occasionally object); indicates possessive (esp. in literary expressions); but; however; still; and

to take (a resource, e.g. time or money); to hang; to come into view; to arrive; to come under (a contract, a tax); to start (engines, motors); to attend; to deal with; to handle; to have started to; to be on the verge of; to overlap (e.g. information in a manual); to cover; to (come) at; to be fastened; to be covered (e.g. with dust, a table-cloth, etc.); to be caught in; to get a call; to depend on

indicates certainty, emphasis, contempt, request, etc.; used when calling out to someone; used to catch one's breath or get someone's attention; yo!