It is not possible to use just a cell phone to create an SD card that will install Ubuntu
First, Not all laptops have SD card readers and even if yours have one, there is no guarantee that your laptop can boot from the SD card.
Second, downloading the file into an SD card using your phone is not enough. The card needs to be prepared using the downloaded file and other software so that your laptop can boot from the SD card. This is not possible using only a cell phone.
Internet and the operating system are not the same thing
Think of your laptop as a car. The operating system is the engine. The internet is all the paved roads in your country and beyond. You don't need the internet to enjoy your car. You can install an air-conditioner in the car. That would be a program in your laptop. Then you can turn the engine on and enjoy the cool air without going anywhere. Your children can turn on the lights, and honk the horn. You can drive it around in your yard, if you have a big yard. But if you have no engine in the car, the air-conditioner, lights, horn will not work. These are different programs in your laptop.
What to do?
If you really need to install Ubuntu in your laptop, you will need a working computer that is connected to the internet. This can be at your friend's home, at an internet cafe, or at a public library (depending on the country you live in). Then you will have to follow the instructions about how to prepare a Live-USB stick using the working computer. When that is ready you will have to follow the instructions about how to boot your laptop using the USB stick you have prepared. This is like changing or putting a new engine in a car. I suggest you read a lot before you try.
Alternately, go to a book store and find a book on Ubuntu. If possible leaf through the book to make sure that if has instructions for how to install Ubuntu. Some of the books include a DVD with Ubuntu in it. If you find one, you can use the DVD to install Ubuntu without the Internet.
Best of luck.