Informal & Affectionate:
* عزیزم، دلم برات تنگ شده (Azizam, del-am barat tang shodeh): "My love, I miss you."
* قشنگم، دلم برات تنگ شده (Qeshangam, del-am barat tang shodeh): "My beautiful one, I miss you."
* جانم، دلم برات تنگ شده (Janam, del-am barat tang shodeh): "My life, I miss you."
More Formal & Romantic:
* عزیز دلم، حسرت دیدنت به دلم مانده (Aziz-e del-am, hesrat didanat be del-am mandeh): "My dearest, the longing to see you remains in my heart."
Note: These phrases are all fairly literal translations. You can make them more natural-sounding by using different words for "baby" (like "عشقم" (Eshgham) - my love) and by changing the tone of your voice.
Additionally:
* You can mention specific things you miss about the person, for example: "دلم برات تنگ شده، صدای خندهت رو میخوام بشنوم (Del-am barat tang shodeh, sedaye khand-et ro mikhaham beshnavam): "I miss you, I want to hear your laugh."
* You can also use a poetic expression to convey your feelings. For example, "مثل پروانه دور شمع میچرخم، تو رو میخوام (Mesle parvane dor sham'e michakham, to ro mikhaham): "I flutter like a moth around a flame, I want you."
It's important to consider the context and your relationship with the person when choosing how to say "Baby I miss you" in Farsi.