Formal:
* ਮੈਂ ਤੁਹਾਨੂੰ ਫੋਨ ਕਰਨ ਵਾਲਾ ਸੀ। (Mai tuhanu phone karan wala si.) This is the most formal and grammatically correct way to say it.
Informal:
* ਮੈਂ ਤੈਨੂੰ ਫੋਨ ਕਰਨ ਵਾਲਾ ਸੀ। (Mai tainu phone karan wala si.) This is a more casual and informal way to say it, using the familiar pronoun "tainu" instead of "tuhanu".
* ਮੈਂ ਤੈਨੂੰ ਫੋਨ ਕਰਨਾ ਸੀ। (Mai tainu phone karna si.) This is similar to the previous one, but uses a slightly different structure.
* ਮੈਂ ਤੈਨੂੰ ਫੋਨ ਕਰਨ ਲੱਗਾ ਸੀ। (Mai tainu phone karan lagga si.) This implies that you were about to call, but something stopped you.
The best option depends on your relationship with the person you are talking to. If you are speaking to someone you know well, you can use the informal forms. However, if you are speaking to someone you don't know well or in a formal setting, it's best to use the formal form.