Overall we have 4 weeks to complete this project, the fact is that it sound “easy” but that does not always make it easier.
That project sounds easy? I think you are drastically underestimating what is involved.
The Arduino wont be a problem, but how do we get it to send data to the phone through a server?
This isn’t the problem. There are multiple ways to make an Arduino communicate with the outside world: ethernet shield, wifi shield, connected to a PC running an application, etc. All of which have a huge number of examples.
We want to make an phone app that can sense if the stove, ironing iron etc. is on/off and if it is on for to long then notify the user
This the part of the project that concerns me. What device are you going to use to sense when each of these appliances is on and count how long it has been on? How will these devices, scattered throughout an area, communicate with the Arduino? Will each sensing device have its own Arduino to communicate with the phone?
Are you going to write a custom application for the phone to communicate with these devices? Or have a (much simpler to implement) web application that pings a server?
I’d suggest narrowing your scope to a single appliance, that plugs into the wall and doesn’t already turn itself off (e.g. Iron). If it plugs into a wall, you might be able to use something like a Kill-A-Watt.