1. The 1st sentence - When did you have it on last? Usually typically refers to "when did you last wear that piece of clothing" for example. When did you last have it. example, "when did you last have your cellphone before you lost it". 2. I've lost my cellphone. Is in the past participle. I lost my cellphone. Is in the present participle.

1. When did you have it on last? This senstence means: have it on= wearing so When did you wear it last? When did you last have it? Refers in general to a possession not necessarily a piece of clothing 2. I've lost my cellphone, it means you've lost it not long ago, it's a present perfect so it's very close to the present moment I lost my cellphone, this sentence is in the past perfect so it happened a while ago Hope it helps

1. The first question implies the person had something "on," either something that can be turned on and off, like a computer, or something that can be put on and taken off, like a shirt. A person fixing a computer might ask this question to find out when the computer stopped working. The second question implies the person lost something. This is a common question to ask when you are helping someone find a lost item. If the lost item is clothing, the two questions are asking the same thing. 2. In the first sentence "have" (contracted to "'ve") suggests that it happened recently. It might also be used for emphasis or to link to the next sentence. For example, someone might say, "I've lost my cellphone again!" Or they might say, "I've lost my cellphone. Can you help me find it?" The second sentence only states the fact. The event could have happened at any time in the past.

Hi Ali. 'When did you have it on last?' can refer to clothing, or if it is also about a phone then the question refers to the time when the phone was turned on. Whereas, the second one is more general and can refer to a number of things e.g. food, or, I'm guessing, it can have to do with the time you were still in possession of something before it was lost. 'I've lost my cellphone' is a present perfect sentence, and therefore, the phone still has not been found. 'I lost my cellphone.' is a past simple sentence and has to do with a past situation. The phone might have been found, but that is not given in the context. For example, "I lost my phone. Luckily, I found it a week later."