Improving indoor mobile phone signal in a high building can be tricky, but there are several options you can explore:

Basic steps:

Contact your mobile network operator (MNO): They might be able to offer solutions like network boosters or femtocells for specific areas with poor reception. Remember, they have an obligation to provide coverage to a large percentage of the population, so your case might qualify for their intervention.

Check your phone and its software: Ensure your phone has the latest software update installed, as it often includes bug fixes and network improvements. Try switching the network mode to prioritize different signal strengths (2G, 3G, 4G, or 5G) depending on your needs. Consider replacing your SIM card if it's outdated.

Solutions depending on signal availability:

If there's a strong outdoor signal:

Signal repeater: This amplifies the existing outdoor signal and rebroadcasts it indoors, boosting your reception. However, be aware that these can sometimes interfere with other networks and require proper installation to avoid legal issues. Check regulations in your area before using one.

Distributed Antenna System (DAS): This involves installing multiple antennas throughout the building to provide better coverage. This is a more complex and expensive solution, but suitable for large buildings with persistent signal issues.

Remember, the best solution depends on the specific situation and available resources. Consider consulting a professional specializing in mobile signal solutions for a more tailored recommendation.

Install the mobile signal booster, it's the most economy way to solve the weak signal problem.