"I will call you now over the phone."
から is used like the word 'from'. It can be used like from Oosaka to Tokyo (大阪から東京まで) or from 10 o'clock untill 11 (十時から十一時まで).
に can be used in various situationa and has a lot of meanings. But, in this sentence the に here is used for 'to' like あなた ' に ' あげます or I will give it 'to' you.
を is used behind the object and infront of the verb. It indicates the object being done by working of the verb in the sentence. Like パンを食べます(I eat a bread).
As far as I could tell, please correct me if I'm wrong. "今から" together is indicating something going to be in this very moment or very soon. "あなたに電話" is defining what the subject is the listener's phone and where "をかけ" comes in to say that the speaker is going to be calling said phone.
I'm not very good at explaining it, but if anybody else can clarify it would be much appreciated!
No, the subject (the one doing the verb) is the implied わたしは. あなたに, as Al0331 pointed out, is the indirect object (who you make the call to), and 電話をかけます means "call (by phone)", which in Japanese is expressed by a transitive verb かけます and a direct object 電話 "phone". An English sentence with similar structure would be "I will now make a phone call to you", but that is kind of stiff and not as natural a thing to say.
今から: Now (technically "starting now", since から means "from")
あなたに: to you (marking the indirect object is one of the uses of に)
電話をかけます: make a phone call (電話 "telephone", を marks the direct object, かけます has various translations in different contexts but here means "call", "make (a call)")
Google translate is not very good for Japanese. Jisho and other similar sites are better.
Here's the definition from the Jsho app
掛ける [かける] 1: to hang (e.g. picture); to hoist (e.g. sail); to raise (e.g. flag) 2: to sit 3: to take (time, money); to expend (money, time, etc.) 4: to make (a call) 5: to multiply 6: to secure (e.g. lock) 7: to put on (glasses, etc.) 8: to cover 9: to burden someone 10: to apply (insurance) 11: to turn on (an engine, etc.); to set (a dial, an alarm clock, etc.) 12: to put an effect (spell, anaesthetic, etc.) on 13: to hold an emotion for (pity, hope, etc.) 14: to bind 15: to pour (or sprinkle, spray, etc.) onto 16: to argue (in court); to deliberate (in a meeting); to present (e.g. idea to a conference, etc.) 17: to increase further 18: to catch (in a trap, etc.) 19: to set atop 20: to erect (a makeshift building) 21: to hold (a play, festival, etc.) 22: to wager; to bet; to risk; to stake; to gamble 23: to be partway doing ...; to begin (but not complete) ...; to be about to ... 24: indicates (verb) is being directed to (someone)
Because the English and the Japanese verbs work a little differently. 電話 (which means just "phone", not "phone number") is the direct object because 電話をかけます is how you say "call (on the phone)" -- basically, "make a phone call". に is used to mark the indirect object (who you make the call to) because the verb already has a direct object (電話).