Could be that your server system get's overheated ... be sure to get an alarm of that ... wherever you are!
Step 1: Unassemble the phone
I got this old Siemens S45 mobile phone. One of these phones where the battery got broken after 1/2 year. While testing with other batteries those small contacts broke and the device got unusable. It still worked. I decided to use the phone for alarmin purpuses on my small Linux server.
Disassembling is not an easy task with this type of phone. You have to find these small plastic "noses" on the left and right side. Best I did to open the case was to slib between the small crack using my fingernails ... some broke during this. But finally the case was open and the parts lay in front of me.