The best way to check coverage for Optus in Mosman is to use the Optus mobile network coverage map and zoom into Mosman. You can access the Optus coverage: https://www.optus.com.au/shop/mobile/network/coverage - You can choose whether to view the coverage around Mosman by 5G, 4G or 3G coverage.
The best way to check the coverage by Telstra in Mosman is to view their coverage maps which are accessible at https://www.telstra.com.au/coverage-networks/our-coverage - You can search and address and see what type of coverage is available. Alternatively pop into the Telstra Shop Mosman and have them show you a coverage map.
Vodafone covers most sizable population areas and major highways. To check Vodafone in Mosman, check out Vodafone's own coverage map: https://www.vodafone.com.au/network/coverage-checker
At present 5G network equipment is still being rolled out. To use 5G you will need a handset that is capable of receiving the 5G signal and also live within an area that has 5G coverage. To check 5G coverage Mosman use the link we have for the coverage maps for your service provider. The aim of 5G network is to enable higher speed transfer for more devices.
If the phone is fairly new and worth quite a few dollars it is probably worth getting it fixed, if you are needing mobile phone repairs Mosman then check out smaller local shops that may offer to do repairs as this may end up being more cost effective than sending your phone back the the manufacturer for repairs.