  Large-scale exoplanet search surveys have shown evidence that atmospheric
escape is a ubiquitous process that shapes the evolution and demographics of
planets. However, we lack a detailed understanding of this process because very
few exoplanets discovered to date could be probed for signatures of atmospheric
escape. Recently, the metastable helium triplet at 1.083 $\mu$m has been shown
to be a viable window for the presence of He-rich escaping envelopes around
short-period exoplanets. Our objective is to use, for the first time, the
Phoenix spectrograph to search for helium in the upper atmosphere of the
inflated hot Jupiter WASP-127 b. We observed one transit and reduced the data
manually since there is no pipeline available. We did not find a significant
in-transit absorption signal indicative of the presence of helium around
WASP-127 b, and set a 90% confidence upper limit for excess absorption at 0.87%
in a 0.075 nm passband covering the He triplet. Given the large scale height of
this planet, the lack of a detectable feature is likely due to unfavorable
photoionization conditions to populate the metastable He triplet. This
conclusion is supported by the inferred low coronal and chromospheric activity
of the host star and the old age of the system, which result in a relatively
mild high-energy environment around the planet.
