Complex sentence: NEST's research showed that younger members would react very negatively to falls in the value of their savings, so in this phase NEST concentrates on steadily building their retirement pot rather than exposing members to unnecessary risk.
Split into simpler sentences: NEST's research showed that younger members may react unfavorably to falls in the value of their savings. So in this phase, NEST concentrates on steadily building their retirement pot rather than exposing members to unnecessary risk.