If Phillips is right then the solution she very clearly described to Adam Boulton on Times Radio last Sunday can be in place in weeks.
Weeks. Software like that doesn't work like that. What she has probably been describing is a very customised locked down 3rd party phone. Getting that 3rd party system integrated into Apple and Google Operating systems is not a matter of "weeks".
Government have not yet defined what they require. Saying "Oh but I saw it working" does not give software engineers enough to work on.
Apple, Google, Samsung, Sony, Motorola, etc. have to sort out ownership, licensing/payment (3rd party software has to be paid for by somebody), interfaces, liability, vulnerabilities, alpha testing, beta developer testing (couple of months), public betas (couple of months), RC release.
eg Apple have just (last few days) done the 1st developer beta release for the iPhone/iPad release due some time in this Autumn. With such a massive user base and low level OS issues can easily "brick" devices testing is not a trivial issue. Consider the impact on eg Apple were they to make a release that included a vulnerability even just "bricked" every iPhone in the UK under some conditions the proposed few days testing didn't catch - the company would never recover.
Companies would also probably now be needing to create UK only special versions of every Operating Systsem release for the UK market as having code taking processor power, battery scanning every screen display 24/7 would be a significant vulnerability/privacy risk and impact sales in every other country in the world.
Issues need to be resolved like most beta testers will be over 18 years old so won't be testing this functionality. Other apps directly access camera hardware which would bypass the "Oh I saw it working" version Ms Phillips saw.
etc., etc.