Great repair on the airframe! I really admire the finish on your model! It was an unfortunate incident, however it does happen. I also used a Phoenix for my L1 cert, but it was a modified Estes Phoenix kit. I used the same thin, flimsy airframe tubing that came with the kit and sent it up on a CTI H133 for my cert flight last year. The flight was successful and came back with no damage and was sent up and back successfully again on a CTI H410. My model was 32 oz loaded and 30 inches in length. All flights were "dumb" flights with no computers and motor eject only. These are the factors I considered for my flights:
1) Environmental: If I don't think my model will go straight up -especially during a cert flight- due to windy or gusty conditions, I will not launch. Observing others' previous flights and noting the direction of ceiling travel (granted there are clouds to observe) as a gauge helps, but I only know what the wind is doing at the ground level. I believe wind to be paramount even to an exact delay adjustment. Any deviation from zenith and the model will be carrying potentially dangerous, zipper-inducing velocity when its cork pops.
2) Delay tuning: Second only to external conditions. Through personal observation I believe improper delay tuning to be the culprit of zippering and other flight anomalies in the majority of otherwise nominal flights. Popular simulators such as OpenRocket and RockSim feature adjustable wind functions. I keep mine low (<5mph) for simulations of which I am seeking a nominal flight or have a model I want to fly once or twice and return to live on as a shelf-queen because I spent so much time and money on the finish. Simulators are your friend in delay adjustment. Keeping the elements of your model as accurate as possible within the program produce the most accurate simulation results whether flying "dumb" or with flight computers.
3) Shock cord length: I used 1/2" kevlar pull tape from Aerocon for the bridle in my Phoenix for its light-weight, heat resistance, high tensile strength and compactness. I used 22' of this tape in my model of 32oz and it fit in the palm of my hand. In my experience, there has been no foul in using lengths of shock cord longer than most would say is necessary. I implement this practice on all of my models. Upon ejection, the sections of my models take their time flying through the air and decelerate greatly before falling into their proper fall profile as the shock cord fully extends even if direction of travel is off vertical and the model is still carrying excessive momentum.
Addendum:
Reading back through your thread I thought I would tack this on.
4) Proper motor selection: As you mentioned, H123 as probably anemic for your flight and would undoubtedly account for poor performance as well especially if wind was a factor. I have yet to learn this lesson the hard way as I tend to go Tim the Tool Man Taylor on my flights and haven't run into inadequate thrust issues. I rarely drop below a 10:1 ratio on my flights and so far we have been sailing smoothly.
Also, are you able to get video of your next cert attempt? Again, congrats on the repair, it looks beautiful! Looking forward to your next flight report. You do great work!
2 cents from a noob.