I have two (Philostacys golden groove and another similar - excuse spelling), which are both about 6 feet tall and seem very 'bushy' - I thinned them out about 3 months ago.

Do I need to thin them out again to encourage them to upwards rather than outwards?

Thanks

Phyllostachys have a general upright habit. Being as your are around 6 ft tall I suspect that they are rather young and could be prone to sending out new culms at angles . This should become less pronounced as each season goes by and the plants mature.It is also possible that the smaller culms do not have sufficient strength to support all the foliage they carry and are inclined to lean or even flop.
The only thinning out I would do at this stage may be the removal of any old or small culms which may enhance the look of the plant.
I would advise against the removal any new growth and pruning of this season's culms.
The culms that have grown this season have most probably reached their mature height and have leafed out. Mine still have some leafing out to do but I live in a cooler part of the country so this is to be expected.
I am unsure of how much knowledge you have concerning bamboo( forgive me if I am stating a fact that you are already aware of) but basically when bamboo starts shooting the new culms attain their mature height in a period of weeks.At this stage of the season you most probably have what you are going to get as far as this season's growth is concerned. My suspicion is that it may be too late to train these angled culms now.
I use the Garden Web U.S. Bamboo forum and have learned an awful lot from that source over the past three months . There are some very knowledgeable people contributing on that forum and I do recall one of the contributors responded to a question regarding training of angled culms.
I would suggest that you post a message on this subject there and I am sure you will receive some ideas.

We have a large leafed bamboo (sorry, don't know the name), the smaller lower 'branches' are sort of falling into our path are we ok to just cut them at ground level (or lower) at this (and any) time of year?

Cheers
ben

It'll probably make the experts wince, but I cut them down to soil level in the autumn and have been doing so for several years. The real hassle is in reducing the rootball if necessary. You need an axe and a chainsaw!!

I am fairly new to bamboo and have not yet found it necessary to get brutal!
Why cut them to the ground in Autumn ?

Am I correct in assuming that by your reference to 'axe & chainsaw' that you may have tried to make some divisions and potted them up ? If so , any success?