"not only directly" is a correct and usable phrase in written English.
It is typically used to emphasize a direct relationship between two things or to introduce a contrast between two related ideas. Example: "Not only did the new regulations directly impact small businesses, but they also caused major disruptions in the industry as a whole."
The video evidence, which not only directly contradicted the accusations but showed the police acting in tandem with the thugs, was, inexplicably, inadmissible in court.
Investment in the public sector not only directly creates real and meaningful jobs but also strengthens resilience in the face of such rapid change.
Increased skin content of ROS not only directly damages the melanocytes but also induces an autoimmune response against them.
Upper computer can read out data not only directly from thermostats, but also from intelligent logging devices.
The transporter probably not only directly enhanced the absorption of xylose but also affected the overall evolutionary trend.
Psychological stress can affect health not only directly through neuroendocrine responses, but also indirectly through changes in health behaviors[13].
In their mounds, ants not only directly produce CO2 by respiration, but may also indirectly impact soil greenhouse gas emissions by affecting substrate availability and soil physicochemical characteristics.
Moreover, the change of surface properties not only directly affects the static bending but also significantly changes the natural frequency of the beam.
Growth factor actions occur not only directly on cells within bone but may also stimulate other tissues, such as skeletal muscle that can indirectly modify skeletal growth.
The pesticide immediately reduced zooplankton density and biodiversity not only directly, by killing copepods, but also indirectly, by increasing the numbers of rotifers.
Thus, cancer not only directly suppresses immune function, but also recruits components of the immune system to become traitors and protect the tumor from immune attack.
