那儿/ 就是 / 我妈妈工作的医院。 That/ is / the hospital hospital which my mother is working for. 就是，is almost the same as 是。 那儿是我妈妈工作的医院。Same meaning to the previous one. 我的手机里/ 有 / 你的电话号码。I have your number in my phone. 有 means something exists in somewhere, or something belongs to someone. 我有一个手机。 I have a cellphone. 你的手机在我这儿，我的手机在你那儿。Your phone is in my place, my phone is in your place. I don't know how to translate "这儿"“那儿”。 it more likes here or there. 在 means something locates at somewhere. 我家前边/ 是 / 北京站。 In front of my home/ is / Beijing Station.