Project phases post-sanction should be minimised if possible
I found that EPCM Designers became so focussed on completing a phase that progress and attention with the following phases usually suffered
A looming construction deadline forces them to check and complete their design
A future construction deadline is then regarded as secondary (less checks/plenty of time in hand) until it also looms
Also construction flushes out design and procurement omissions. Resolving these issues for subcontractors usually requires resources which have moved on to the following phase
Client teams are also affected due to having to be periodically mobilised and then demobilised
However the impact of project phases could be minimised with robust project management of deliverables and issue resolution