I do not think Bitcoin needs significant improvements in the future because it's good as it is. Your comparison is not very good with upgrading to your phone. Upgrading to the phone comes from the need for greater security against hacking. Bitcoin uses a decentralized system, and hacking is almost impossible. The only "upgrades" that can be made are trading exchanges, both for their security and investor investment, as well as adjustments to transaction taxes.
No, bitcoin will need significant improvements in the future if it's necessary because if bitcoin is not doing that, then bitcoin cannot serve the best works for us.
Upgrading the phone is necessary if we want to get a new update from the developer so we could get better apps for our phone.
Yes, the exchanges must be upgraded the security from time by time because they need to protect the member, the asset, and the website itself. Without making an update for the exchanges, we will see there will be many hacker cases in the future that will happen.